docs: def add_pre(h,sec_list,section,order_list=None,branch_order=None):
      """
      A helper function that traverses a neuron's morphology (or a sub-tree)
      of the morphology in pre-order. This is usually not necessary for the
      user to import.
      """
  
      sec_list.append(section)
      sref = h.SectionRef(sec=section)
  
      if branch_order is not None:
          order_list.append(branch_order)
          if len(sref.child) > 1:
              branch_order += 1
      
      for next_node in sref.child:
          add_pre(h,sec_list,next_node,order_list,branch_order)